1. Field of the Invention
The present invention relates to a piezoelectric ceramic, a vibrator and an ultrasonic motor.
2. Related Background Art
Piezoelectric ceramics for use in ultrasonic motors, ultrasonic washers and piezoelectric transformers, and piezoelectric ceramics of piezoelectric actuators using resonance displacement are desired to have large resonance displacement and excellent piezoelectric properties. Particularly, when a piezoelectric ceramic is applied to the aforementioned uses, the drive frequency is high. Accordingly, if the mechanical quality factor (Qm) of the piezoelectric ceramic is low, heat easily generates and, for example, depolarization occurs and piezoelectric properties may change. For this reason, a piezoelectric ceramic having a sufficiently large mechanical quality factor (Qm) has been desired.
As a piezoelectric ceramic satisfying such properties, a perovskite-type compound such as a PZT (PbZrO3—PbTiO3 solid solution)-based compound and a PT (PbTiO3)-based compound have been used (see, for example, Japanese Patent No. 3785648). However, since such a piezoelectric ceramic contains Pb, an environmental issue is a matter of concern. Therefore, various studies have been conducted on Pb-free compositions of a piezoelectric ceramic. For example, BaTiO3-based and KNN (KNbO3—NaNbO3 solid solution)-based piezoelectric ceramics have been proposed (see, for example, Japanese Patent Application Laid-Open No. 2003-055048).